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Received Nov 27, 2017; Accepted Feb 7, 2018
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1. Introduction
Alzheimer’s disease is characterized by the pathological accumulation of amyloid-β (Aβ) peptides and tau protein, leading to the formation of neurofibrillary tangles and the loss of neuronal cells. Amyloid beta, a 39–43-amino acid residue peptide, is found in the healthy human brain and is considered to have a normal physiological role. It exists as Aβ fibrils because of cleavage from a larger amyloid precursor protein [1]. In AD, the accumulation of amyloid fibrils as amyloid plaques or senile plaques in extracellular region of brain cells is closely linked to the loss of synapses, synaptic dysfunction, inflammatory responses, and neuronal loss. On the other hand, tau protein or T proteins are found abundantly in definite spatial patterns in the entorhinal cortex followed by hippocampal and cortical areas of the central nervous system and plays a vital role in stabilizing microtubule. In AD pathology, the tau protein undergoes intense hyperphosphorylation, leading to the clumping of tau protein, which forms intracellular neurofibrillary tangles (NFT). The intracellular formation of NFT leads to microtubule disassembly, dendritic spinal collapse, and the degeneration of axons. The pathological aggregation of intracellular NFT and extracellular senile plaques precede the initial signs of cognitive impairment in mild AD patients by at least 10–20 years. Mild signs of AD include memory loss, mood changes, nervousness, difficulty in handling money, and poor judgement. However, in late-stage AD, patients will need full time, around the clock assistance as more severe cognitive alterations, such as a loss in the ability to respond to the environment, confusion, restlessness, and difficulty with language and thoughts, as well as difficulty in the control of movement, will be experienced by patients [2].
2. Common Neurodegenerative Mechanisms in AD
2.1. Mitochondrial Dysfunction and ROS Production
Neurons in the human brain have tremendous oxygen consumption and metabolic rates. For this reason, neurons rely on mitochondria that are found in abundance in brain tissues for the production of energy by oxidative phosphorylation. Mitochondria are the central sites of ROS, as natural byproducts...